The metabolic transformation of arylamines and nitroaromatics in selected types of microbial systems is under investigation. Particular interest has been given to the conversion of these types of organic chemicals into the nitroso oxidation level. Previous work by this investigator has established that aromatic nitroso compounds are partially converted into aromatic hydroxamic acids by means of the action of certain thiamine dependent enzymes. The possibility that similar pathways are operative in certain microbial species will be examined.